Early probe of the Sago disaster raises explosive questions

Was the safety of the mine compromised by the pipeline running over the top? That pipeline carried highly volatile natural gas across the top of a mine that used large amounts of electricity for cutting coal. Its proximity raises the possibility, however slight, that it could have contributed to the disaster. And as the Charleston Gazette has reported, the mine is close to several bore holes of abandoned gas wells. Sometimes such bore holes contain substantial amounts of methane, which can cause an explosion if struck by mining machinery. Many of these wells are mapped, but some are not, and the maps aren't always accurate.

Why had that part of the mine been sealed in an unusual way? Traditionally, miners use concrete blocks to seal off sections, but the accident occurred in an area where weaker blocks of fly ash had been used instead. These blocks, approved by the state inspector last December, were blown out in the explosion. Why were they approved and did they contribute to the miners' deaths?